Inflation devices are commonly used by the medical profession in different applications, such as angiography and angioplasty procedures. Many of the inflation devices are simple in design, and mass produced from a plastic material. These basic inflation devices include a cylinder having a proximal end opening, a fluid conduit at the distal end which is adapted to be connected to a balloon, and a shaft and piston inserted within the proximal end of the cylinder for forcing fluid out of the fluid conduit when the piston shaft is extended into the cylinder.
Typically, simple syringes used as inflation devices are not designed to precisely control the amount of fluid discharged to the balloon. As a result, the devices are inadequate for many angioplasty procedures in which the pressure within the balloon must be precisely controlled. Angioplasty procedures require an inflation device that will accurately pressurize the balloon. Additionally, it is advantageous for an inflation device to allow the balloon to be selectively deflated during the procedure.
Various proposed inflation devices used in angioplasty and similar procedures provide for selective and controlled inflation and deflation of the balloon. For example, U.S. Pat. No. 4,583,974 to Kokernak discloses an inflation device for use in angioplasty in which a threaded half nut latch is pivotally attached to the cylinder. The shaft is threaded and the latch is manually moved between a disengaged position in which the shaft is free to move axially within the cylinder and an engaged position in which the half nut extends through a slot opening in the barrel to engage the threaded shaft to lock the shaft in position. In this locked position, the shaft is rotated to move the shaft within the cylinder.
U.S. Pat. No. 5,057,078 to Foote et al. discloses another inflation device in which a hand-held trigger is secured to the device handle to actuate sliding channels and a spring to force a threaded rack out of engagement with threads positioned on the interior surface of the cylinder. When the threads are engaged, the handle can be turned and the piston shaft may be incrementally moved within the cylinder to enable controlled pressurization. When the piston threads are not engaged, the piston shaft is unlocked and free to move axially within the cylinder.
Although these proposals provide an inflation device in which the piston shaft can be locked or unlocked for either controlled, incremental movement or free, axial movement within the cylinder, the proposed designs do not offer a mechanism for controlling locking and unlocking of the piston shaft which takes advantage of the cylindrical design of the inflation device. The cylindrical configuration of the cylinder and piston shaft can accommodate designs in which simple, rotatably movable components such as cams, cam followers, and semicircular shaped half nuts can be mounted within the cylinder and actuated by means external to the cylinder, such as a collar or the piston shaft itself. These mechanisms can in turn reliably lock and unlock threaded locking assemblies. Many locking mechanisms used with cylindrically configured inflation devices typically use racks or pivoted assemblies which are more complex, expensive, ergonomically inefficient, or difficult to use than the more desired rotatably movable components such as cams, cam followers, and half nuts.